Generally, braking systems for a recreational towed vehicle such as a travel trailer or the like operate based on electric signal derived from a towing vehicle that controls the electric power of electro-motive force (EMF) applied to a solenoid or the like to adjust the braking pressure applied by the solenoid to the brake pad of the trailer brake.
It is also common practice to use what is known as a surge brake which mounts on the tongue and applies braking pressure based on the pressure exerted between the towed vehicle and the towing vehicle to apply the appropriate braking pressure to the hydraulic brake cylinders in the towed vehicle.
In larger trailers such as semi-trailers or the like, the interconnection between the towing vehicle and the towed vehicle is generally pneumatic and the pneumatic pressure is used to apply the appropriate braking forces to the trailer wheels. These systems generally include some form of fail safe provision, for example, if a pneumatic pressure falls below a specific level, a mechanical braking system on the trailer is released and locks on.
Electric braking systems are weak in that the maximum braking pressure that may be applied to the brake pads is limited. This type of brake requires an electric input e.g. an EMF or the brakes cannot be applied, thus, they are not fail safe (cannot apply braking force if the power is cut off) unless a suitable source of power is available on the towed vehicle and is activated when the EMF from the towing vehicle is cut-off or disconnected.
U.S. Pat. No. 3,768,870 issued Oct. 30, 1973 to Howard describes an electrically controlled hydraulic braking system for a towed vehicle. In this system a pump is used to generate the hydraulic braking pressure in the towed vehicle and the applied brake pressure in the towed vehicle is compared with the brake pressure in the tractor or towing vehicle and the pressure in the towed vehicle is modulated to correspond with that in the towing vehicle. This system is relatively complex and has no fail safe feature.
U.S. Pat. No. 5,129,712 issued Jul. 14, 1992 the inventors Feldmann et al. discloses a braking system wherein the braking pressure applied in the towing vehicle is transformed into an electrical signal and the electric signal is used to modulate the pressure applied in the braking system on the towed vehicle. This system is also not a fail safe system.